Long chain polyunsaturated fatty acid synthesis in a marine vertebrate: Ontogenetic and nutritional regulation of a fatty acyl desaturase with Δ4 activity

Abstract

Solea senegalensis is an unusual marine teleost with very low dietary requirement for longchain polyunsaturated fatty acids (LC-PUFA) during early development. Aquaculture is rapidly becoming the main source of health-beneficial fish products for human consumption. This, associated with limited supply of LC-PUFA-rich ingredients for fish feeds, render S. senegalensis a highly interesting species in which to study the LC-PUFA biosynthesis pathway. We have cloned and functionally character -3 series) and elovl5 with the potential to catalyze docosahexaenoic acid (DHA) biosynthesis from eicosapentaenoic acid (EPA). Changes in expression of both transcripts were determined during embryonic and early larval development, and transcriptional regulation in response to dietary n-3 LC-PUFA was assessed during larval and post-larval stages. There was a marked pattern of regulation during early ontogenesis, with transcripts showing peak expression coinciding with the start of exogenous feeding. Although elovl5 transcripts were present in fertilized DHA/EPA ratio (~ 11) to meet the high demands for early embryonic development. Fatty acid profile was significantly up-regulated in response to LC-PUFA-poor diets, which may suggest biological relevance of this pathway in reducing LC-PUFA dietary requirements in this species, compared to other marine teleosts. These results indicate that sole is capable of synthesizing DHA from EPA through a Sprecher-independent pathway. Suggested Reviewers: Xiaozhong Zheng xzheng@staffmail.ed.ac.uk Dr Zheng has done considerable work involving cloning and functional characterization of Fads and Elovls in fish and is therefore a very specific expert in this field.Johnathan A. Napier jon.napier@bbsrc.ac.uk Prof. Napier is an expert in Fad molecular biology and has considerable expertise in pathways of DHA biosynthesis.Chantal Cahu Chantal.Cahu@ifremer.fr Dr. Chantal Cahu is an expert in marine larvae nutrition including fatty acid metabolism. In addition, she has also been involved in molecular and genomic studies, including the cloning and Fad expression in fish.Gabriel Mourente gabriel.mourente@uca.es Dr. Gabriel Mourente is an expert in marine larvae nutrition including fatty acid metabolism. He has additionally performed several larval nutrition studies in S. senegalensis and has also worked specifically with enzymes of the pathway of LC-PUFA biosynthesis.Manuel Yúfera manuel.yufera@icman.csic.es Dr. Manuel Yúfera is an expert in marine larvae nutrition including fatty acid metabolism and has additionally performed several larval nutrition studies in S. senegalensis. Fatty acyl desaturase and elongase cDNAs corresponding to a 4fad (with some 5 activity for PUFA of the n-3 series) and elovl5 were cloned from a marine teleost (Solea senegalensis) and functionally characterized by heterologous expression in yeast. Historically, it was believed that the pathway for DHA synthesis would involve a 4 desaturase, as this would be the most direct route, but the presence of 4Fad enzymes cou...

Omega-3 long-chain polyunsaturated fatty acids and aquaculture in perspective

“…A discrete Δ5 Fad has only been isolated from Atlantic salmon although bifunctional Δ6Δ5 Fads have been characterised in zebrafish, rabbitfish, Siganus canaliculatus and Mexican silverside, Chirostoma estor (Hastings et al, 2001;Li et al, 2010;Monroig et al, 2014). The presence of Δ4 Fad enabling direct production of 22:6n-3 from 22:5n-3 has been demonstrated in rabbitfish, Senegalese sole, Solea senegalensis and Mexican silverside, Chirostoma estor (Li et al, 2010;Morais et al, 2012c;Monroig, et al, 2014). The Sprecher shunt pathway via C24 fatty acid intermediates has been shown in trout (Buzzi et al, 1997) and the Δ6 Fad of Atlantic salmon and zebrafish can operate on both C18 and C24 fatty acids .…”

Diversification of substrate specificities in teleostei Fads2: characterization of Δ4 and Δ6Δ5 desaturases of Chirostoma estor

“…First, the so-called "Sprecher pathway" involves two sequential elongation steps from EPA to 24:5n-3 and a subsequent ⌬ 6 desaturation to 24:6n-3, followed by peroxisomal chain shortening ( 3 ). Second, a more direct pathway has been postulated in some marine fi sh that involves elongation of EPA to docosapentaenoic acid (22:5n-3) followed by ⌬ 4 desaturation to DHA ( 4,5 ).Dietary PUFAs are essential in fi sh, although requirements vary with species ( 6, 7 ). Generally, C 18 PUFAs can satisfy essential FA requirements of freshwater and salmonid species, but most marine fi sh have a requirement for LC-PUFAs such as EPA and DHA ( 8 ).…”

Roles of lipids and fatty acids through the spermatogenesis of European eel (Anguilla anguilla)

“…Different fish species have different ways of increasing PUFA to maintain the structural and functional integrity of their cellular membranes (Farkas et al, 2001). Recently, this widely accepted paradigm was revised after the discovery of another pathway of synthesis of LC-PUFA in two marine vertebrates, Siganus canalicalatus (Li et al, 2010) and Solea senegalensis (Morais et al, 2012) so, further investigations would be needed to find different biosynthesis pathways. After observing the great ability of the eel to synthesize PUFA in the liver during spermiation, studies on the isolation, cloning, and characterization of European eel fatty desaturases and elongases should be an important focus of future research.…”

“…Table 1. Bioconversion ability of 18:3-n3 (Kanazawa et al, 1979) In recent years, numerous studies on the abilities of fatty acid bioconversion in freshwater and marine fish have been carried out (Monroig et al, 2012Morais et al, 2012;Fonseca-Madrigal et al, 2014). It has been demonstrated that a freshwater fish may have a marine pattern of fatty acid elongation and desaturation or vice versa.…”

“…The synthesis of LCPUFA occurs in the microsomal fraction of the liver except for the chain shortening from 24:6-n3 to 22:6-n3 and from 24:5-n6 to 22:5-n6, which occurs in the peroxisomes by β-oxidation (Figure 4) (Monroig et al, 2011). Recently, an alternative more direct way for DHA biosynthesis has been shown by the presence of fatty acyl desaturase with Δ4 activity, demonstrating that an alternative pathway via direct Δ4-desaturation of 22:5-n3 was possible for the production of DHA from EPA in two marine fish (Siganus canaliculatus; Li et al, 2010 and Solea senegalensis;Morais et al, 2012). …”